One type of memory currently of interest utilizes magnetic tunneling junctions in the memory cells. A magnetic tunneling junction typically includes two ferromagnetic layers separated by a thin insulating layer. The insulating layer is thin enough to allow charge carriers to tunnel between the ferromagnetic layers. One ferromagnetic layer has its magnetization fixed, or pinned, in place. This is typically accomplished using an antiferromagnetic layer. The other ferromagnetic layer has a magnetization that can rotate in response to an applied magnetic field. The resistance of the magnetic tunneling junction depends upon the orientation of the magnetic tunneling junctions. Thus in order to store data in the magnetic tunneling junction, a magnetic field is applied to rotate the magnetization of one of the layers. Typically, the magnetization of one ferromagnetic layer will be rotated to be parallel or anti-parallel to the magnetization of the other ferromagnetic layer. The magnetic tunneling junction will thus be in either a low resistance (magnetizations parallel) or a high resistance (magnetizations antiparallel) state to represent a “0” or a “1”, respectively. A signal corresponding to the resistance is developed in order to indicate the value of the data stored.
In order to utilize magnetic tunneling junctions for storage, the magnetic tunneling junctions should be shielded from stray magnetic fields. If the magnetic tunneling junctions are not shielded, then stray magnetic fields might alter the data stored in the magnetic tunneling junction. Consequently, U.S. Pat. No. 5,902,690 describes the use of insulating ferrite materials to shield magnetic tunneling junctions from stray fields.
Although the ferrite materials may provide some shielding for the magnetic tunneling junctions, one of ordinary skill in the art will readily recognize that the ferrite materials have a relatively low saturation magnetization. As a result, the insulating ferrite materials may not be capable of responding to some of the stray fields to which the magnetic tunneling junctions are exposed. Consequently, the ferrite materials may not be able to shield magnetic tunneling junctions used in a magnetic memory. Thus, the data stored in the magnetic memory may be lost.
Accordingly, what is needed is a system and method for providing a magnetic memory cell having improved shielding. The present invention addresses such a need.